Purpose: Stereotactic radiosurgery (SRS) and fractionated SRS (fSRS) have become emerging treatment options for multiple brain metastases, reducing neurocognitive risks compared with conventional whole brain irradiation. Brainlab Elements (DCA) and Varian RapidArc (VMAT) are both widely used in LINAC-based SRS planning, and have been compared previously by others. However, existing studies have focused on small-to-moderate numbers of lesions, usually <5. We aim to dosimetrically compare the plan quality between the two techniques for SRS of large numbers of brain metastases, >20 lesions, as these cases become increasingly commonplace in clinical practice.
Methods: Six patients with 20 to 36 brain metastases (total 159, median 26, Vmin = 0.04 cc, Vmax = 12.24 cc) were retrospectively planned with single-isocenter DCA and VMAT by experienced SRS planners following institutional planning standards. All plans used 6MV flattening-filter-free beam on Varian Edge equipped with HD-MLC. DCA used double-pass 7 non-coplanar arcs and VMAT used 7 non-coplanar arcs. Original prescriptions of 24-27Gy in 3-5 fractions were used and all plans were normalized to 95% of PTV receiving the prescription dose. Plans were evaluated using the Paddick Conformity Index (CI), normal brain exposure >X Gy (Vx), and organ-at-risk (OAR) maximum point dose.
Results: All plans achieved clinically acceptable OAR dose constraints. VMAT achieved superior conformity than DCA for all cases and the median difference was 23.7%. Lower total monitor units were also observed for VMAT than DCA plans, differing by >2 fold. However, all normal brain dosimetric parameters (V12Gy, V8Gy, V5Gy, and mean dose) were lower with DCA, with median differences of 10.1%, 20.7%, 12.4%, and 6%, respectively.
Conclusion: For LINAC-based single-isocenter brain fSRS with a large number of metastases, VMAT plan is capable of achieving superior conformity with significantly minimized beam-on time and monitor units. DCA plan facilitates reduced normal brain doses compared with VMAT plan.
Stereotactic Radiosurgery, Dosimetry, Treatment Planning